1. Field of the Invention
The present invention relates to a mobile radio communication equipment and, particularly, to a mobile radio communication equipment having a function of regulating a sound volume of voice which is being listened by a user of the mobile radio communication equipment.
2. Description of Related Art
In a conventional mobile radio communication equipment having a function of regulating a sound volume of voice which is being listened by a user of the equipment, the sound volume is regulated by the user himself by manually operating a volume key preliminarily provided on the equipment so that the sound volume of listening voice becomes desirable regardless of existing environmental noise.
In such conventional radio communication equipment, however, when a sound volume on a transmitting side is small, there is a possibility that a sound volume on the receiving side becomes small necessarily, so that the user on the receiving side must manually operate the volume key, resulting in that a convenience of the user is lost. Further, the user must manually operate the volume key every time the sound volume and/or ambient noise on the receiving side varies, resulting in low operability of the equipment.
Under such circumstances, a mobile radio communication equipment provided with a noise sensor for detecting background noise has been proposed in, for example, Japanese Patent Application Laid-open No. Hei 4-822331, in which a background noise level detected by the noise sensor is compared with a threshold value based on a signal input from a key pad and a receiving sound volume of a loud-speaker is regulated correspondingly to a result of the comparison.
Further, another mobile radio communication equipment has been proposed in, for example, Japanese Patent Application Laid-open No. Hei 7-307697, in which an average value of an audio signal output from a transmitter is compared with a reference level of ambient noise, it is recognized whether or not the audio signal output from the transmitter is a transmitting sound and a receiving sound volume is automatically regulated correspondingly to the ambient noise level by controlling a gain of a variable gain amplifier for amplifying the receiving sound, on the basis of a result of the comparison and a result of the recognition.
In the former one of the above mentioned conventional mobile radio communication equipments, which is provided with the noise sensor, it is possible to automatically regulate according to the ambient noise level. However, the noise sensor dedicated to ambient noise detection must be additionally provided to the transmitter/receiver. Therefore, the number of parts of the mobile radio communication equipment is increased and a space for mounting the noise sensor is necessary in the mobile radio communication equipment, which are inconvenient for the mobile radio communication equipment which should be compact and light-weight.
According to the latter one of the conventional mobile radio communication equipment, it is possible to automatically regulate the receiving sound volume according to the level of ambient noise. However, it is necessary to confirm from the transmitting audio signal output whether or not the transmitting audio signal is a transmitting sound. In order to do so, the average value of the output audio signal from the transmitter is compared with the audio signal. However, depending upon the volume of the ambient noise, it is impossible to exactly know whether or not the audio signal is the transmitting sound. Therefore, there may be an error of receiving volume regulation, causing a problem in reliability to occur. Further, it is impossible for individual users to regulate the sound volume to values optimal for them.